1. Technical Field
The disclosure relates to a circuit board and a ground line structure. Particularly, the disclosure relates to a flexible circuit board and a ground line structure.
2. Related Art
Along with development of electronic technology, various electronic products are widely used in people's daily life and work, especially the most commonly used electronic produces such as information products and home appliances, etc. In order to implement a specific function, the electronic product generally includes a printed circuit board in collaboration with a proper circuit layout to implement the specific function. The printed circuit board generally transmits electrical signals through a ground line structure and a signal line structure therein. Based on different applications, the printed circuit boards are usually grouped into rigid printed circuit boards and flexible printed circuit boards. The rigid printed circuit board generally uses a whole slice copper thin film layer as the ground line structure, and the signal line structure is disposed thereon, and the ground line structure and the signal line structure are used in collaboration to transmit electrical signals.
However, in an application of the flexible printed circuit board, the whole slice copper thin film layer may decrease flexibility of the printed circuit board. Therefore, according to the conventional technique, the ground line structure is designed in a meshed pattern to achieve flexibility of the flexible printed circuit board. However, the design of the meshed pattern may result in a fact that different signal lines of the signal line structure have different impedances relative to the ground line structure, which leads to a great difference in propagation delay between the signal lines. Taking a differential signal as an example, if the difference of the propagation delays is too large, besides a problem of signal skew, an excessive common mode noise is also generated.